The present invention relates generally to an antenna for conveying communication signals in the radio frequency (RF) range and, more particularly, to an antenna operating at radio frequencies around 2.45 GHz.
A Bluetooth system provides a communication channel between two electronic devices via a short-range radio link. In particular, the Bluetooth system operates in the radio frequency range around 2.4 GHz in the unlicensed Industrial-Scientific-Medical (ISM) band. The Bluetooth radio link is intended to be a cable replacement between portable and/or fixed electronic devices. The portable devices include mobile phones, communicators, audio headsets, laptop computers, other GEOS-base or palm OS-based devices and devices with different operating systems.
The Bluetooth operating frequency is globally available, but the permissible bandwidth of the Bluetooth band and the available RF channels may be different from one country to another. Globally, the Bluetooth operating frequency falls within the 2400 MHz to 2497 MHz range, corresponding to a wavelength range of 120 mm to 125 mm in free space. In free space and for a xc2xcxcex antenna, the physical length of the radiating element for a Bluetooth antenna is equal to the electric length of 30 mm to 31.25 mm. But when the antenna is installed in a device, the relative permittivity of the materials surrounding the antenna greatly reduces the physical length of the radiating element.
Even with a radiating element shorter than 30 mm, integrating such an RF antenna into an electronic device remains a major challenge in the design of the device. The antenna needs some space around it in order to operate properly. The antenna cannot be enclosed inside the chassis of the device. Furthermore, the RF components related to the antenna must be properly shielded from other electronic components of the device.
Presently, small-sized radio-frequency antennae are designed based on a planar configuration. For example, European Patent Application 0 623 967 A1 discloses a planar antenna operating in the 915 MHz band. This antenna consists of an L-shaped planar resonator part, a feed pin and a grounding pin joining the resonator part at one end thereof. U.S. Pat. No. 5,929,813 discloses an antenna which is operating in the frequency range of 824 MHz-894 MHz and is constructed from a single sheet of conducting material. While the above-described planar antennae are useful for their intended purposes, they are difficult to be integrated into a portable device such as a communicator device which operates in both the cellular frequency and the Bluetooth frequency.
It is advantageous and desirable to provide a small antenna so that it can be integrated into small electronic devices such as mobile phones, communicators and miniaturized audio headsets to provide a radio link in the Bluetooth band and other radio frequency bands.
The radio frequency (RF) antenna, according to the present invention, includes a non-planar resonating region made from an electrically conducting material for radiating or receiving electromagnetic waves. In a non-planar configuration, the resonating region is folded such that the main radiating surface of the antenna consists of at least two sections located in different planes. This is in contrast to a planar configuration where the main radiating surface of the antenna is located substantially on the same plane. Because the main radiating surface is folded into sections, the size of the antenna is greatly reduced, allowing the antenna to be integrated into mobile phones, communicators or other miniaturized electronic devices.
The resonating region has an electric length substantially equal to one quarter of the wavelength of interest in free space. To be used in a Bluetooth device having a radio link operating at approximately 2.45 GHz, the electric length of the radiating element is approximately 30.6 mm. However, the physical length of the radiating element is approximately 21 mm, depending on the relative permittivity of the materials surrounding the radiating element.
Preferably, the antenna also includes a feeding region coupled to the resonating region for impedance matching. The feeding region includes a feed pin and a grounding pin joining the resonating region at one end thereof. As the resonating region is used to radiate or receive electromagnetic waves carrying communication signals or messages, the feed pin which is joined to the resonating region at a feed point serves as a signal conduit between the resonating region and the RF processing components in the device. The grounding pin which is joined to the resonating region at the proximity of the feed point is used to match the input impedance of the antenna which is typically 50xcexa9.
Preferably, the antenna is mounted on a printed-circuit board (PCB) with the resonating region seated on a plastic block. In a mobile phone or a communicator, it is preferred that the antenna is mounted on the system connector adjacent to the bottom connector pins. The grounding pin and the feed pin can be produced by splitting an extended portion of the resonating region, but they can also be part of the circuit on the PCB.
The antenna, according to the present invention, will become apparent upon reading the description taken in conjunction with FIGS. 1-9.